1. Field of the Invention
The present invention relates to a tomography technique, particularly to a tomographic apparatus for obtaining a cross-sectional image by fixing an X-ray source and by synchronously rotating an object under examination with a detector. The present invention also relates to a method of obtaining a cross-sectional image of a three-dimensional object from an arbitrary angle and height by computational calculation utilizing the tomographic apparatus.
2. Description of the Prior Art
A tomographic apparatus is utilized in diverse fields. In the field of electronics, the tomography is particularly used for monitoring a soldering state on a substrate of an electronic circuit. The conventional methods of monitoring a soldering state by utilizing X-ray tomography can be roughly classified into two.
One method is a laminographic method for acquiring a cross-sectional image with a single image by synchronously rotating an X-ray source and a detector, and the other method is a digital tomosynthetic method for obtaining an average value of the images acquired during rotating an X-ray source in a computer.
U.S. Pat. No. 5,081,656 issued on Jan. 14, 1992 to Baker et al. discloses a laminography system utilizing a laminographic method. FIG. 1 briefly illustrates the example.
Referring to FIG. 1, an object under examination 1, a circuit substrate for instance, is laid in the middle of an X-ray source 2 and a detector 3. An image plane 6 of the object 1 is formed on a detector 3 by projecting an X-ray beam onto the object 1 from the X-ray source 2 synchronized around a common axis 4 and the detector 3. Particularly, the image plans 6 substantially lies in parallel with the planes 8, 9 defined by rotation of the X-ray source 2 and the detector 3.
Such a laminography utilizing the conventional laminographic method requires an X-ray tube which will rotate the X-ray source only to electronically rotate an X-ray beam. However, the X-ray tube is not only expensive but also generates a cross-sectional image of low precision due to the slope angle of the beam fixed to be under 30.degree.. Also, the obtained cross-sectional image is unclear and is of low resolution.
U.S. Pat. No. 4,688,241 discloses a digital tomosynthetic method. Referring to FIG. 11 of U.S. Pat. No. 4,688,241, an X-ray source is projected (T1 to T8) while rotating in circle 480. This method is identical to the aforementioned method of projecting an X-ray in the laminography. A focus plane 484 of an object 456 is projected to the entering plans 494 of a large-scaled image amplifying tube 490. An image formed on a camera 494 is processed by a computer 500. This method has an advantage of processing the image in a digital value but requires an expensive scanning tube. Also, the cross-sectional image generated by this method is of low precision because the slope angle of the beam cannot be greater than 30.degree.. The apparatus employing a large-scaled image amplifying tube (12") is expensive. Further, the image acquired by utilizing the periphery of the image intensifier of spherical shape is highly distorted.